This invention relates to the generation and display of computed images, and more specifically, to visual presentations finding application in aircraft flight simulators. While the invention is described in particular detail with respect to such visual simulation use, those skilled in the art will recognize the wider applicability of the inventive principles disclosed hereinafter.
The U.S. Pat. No. 3,996,673, to Vorst et al, describes an apparatus for generating computed images on an electrically controlled display means. The entire disclosure of U.S. Pat. No. 3,996,673 ('673) is incorporated herein by reference. In the '673 patent, a particular device which provided the shading required for realistic image enhancement was disclosed. The means for varying the intensity of an image formed on a raster display disclosed in the '673 patent was operated by interpolating a known, required intensity set at the four corners of the display, and assigning an intensity value for each raster line between the top and bottom based on that interpolation. While the device and method disclosed in the '673 patent works well for its intended purpose, the embodiment disclosed did not lend itself to all simulation aspects. In particular, low visibility effects are an important part of visual simulation. Low visibility, in order to be realistic in the simulator context, should have similar effects on light points displayed in the image, and other surface attenuation. Intensity extinction positions for both should be well controlled. In addition, it is desirable to provide a smooth transistion from ground imagery to ground haze to sky, over a relatively narrow band of the display area, in order to enhance the image in a realistic manner.
The intensity interpolation utilized in conjunction with the '673 patent, while working well for its intended purpose, is not easily adaptable to the problems present with ground haze sky transition present in the art and described above.
It is possible to define, store and display in real time the intensity for each picture element (pixel) in a visual simulation system based on individual pixel digital processing, even though this is an extremely complex process. In a visual display system based on an image related scan, the process becomes exceedingly difficult because of the lack of pixel "bookkeeping". That is to say, as the picture drawing beam moves between the boundaries of the surface being drawn, the exact coordinates of the beam at a particular instance in time are not available in digital form.
The raster line shader described herein solves the problem of low visibility "effects" generation for an image related scanned simulation system. The invention disclosed hereinafter computes and displays intensity without need for individual pixel processing. The raster line shader uses digital computations which provides the needed accuracy providing low visibility effects and an earth sky haze band. These computations take advantage of the approximately constant intensity over a raster line when the raster line is parallel to the simulated horizon.
One of the objects of this invention is to provide an improved raster shader for a computer generated display.
Another object of this invention is to provide a device which produces an improved shading function for a computer generated display.
Another object of this invention is to provide a raster shading device which is compatible with aircraft simulators presently being sold commercially.
Another object of this invention is to provide a low cost shading device for an image generator.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.